Converter circuits are generally known in the art. For example, DC to DC converter circuits accept a DC voltage input and in turn provide an output of a different DC voltage. One type of DC to DC converter circuit is a buck converter circuit, which typically receives a higher voltage signal and outputs a lower voltage signal. Buck converter circuits generally operate in one of two modes, a continuous mode and a non-continuous mode. A buck converter circuit typically transitions from a continuous mode to a non-continuous mode to improve efficiency. For example, when the output load condition for the converter circuit decreases significantly such that less input energy is needed to maintain a regulated DC output, a buck converter circuit may change from the continuous mode to a non-continuous mode to reduce switching losses associated with continuous mode. In the non-continuous mode, the circuit will then only occasionally provide energy or burst energy to provide the necessary output when the output load drops.
Transitions between the continuous and non-continuous mode, however, often cause output voltage transients that are undesirable. These output voltage transients are different from those induced in a converter running in one mode all the time. For instance, a converter operating in continuous mode remains in steady state so long as there are not any output load step changes, whereby steady state results in a well regulated output voltage. Load step changes while maintaining continuous mode are often designed around and minimized using established methods in power supply design. When a converter, however, changes modes, output transients can become unpredictable due to a control loop change. For example, a converter switching from an efficiency savings non-continuous mode to a continuous mode in response to an increase in output load, can exhibit a significantly larger output voltage transient, overshoot or undershoot, than a converter incurring a load step while during a continuous operation. In this case, common power supply design techniques that handle load transients in a single continuous mode do not work for situations involving mode transition.
Current mode control converters that use transconductance output error amplifiers have implemented methods to minimize output voltage disturbance upon mode change. These error amplifier outputs reflect load current during continuous mode. In non-continuous control, some techniques have been implemented that condition the output of the error amplifier in anticipation of mode change back to continuous control. Voltage mode control converters that use voltage error amplifiers exhibit a different and unique challenge from current mode control converters. The output voltage of the error amplifier in a voltage mode converter reflects the duty cycle, or output voltage to input voltage conversion ratio, during the continuous mode. Often the error amplifier is not used for control during non-continuous mode. Upon engaging it back into the control loop when transitioning from non-continuous to continuous, its output voltage could exhibit significant change leading to significant converter output transient. A new method is herein described to address this problem and minimize the converter output voltage transient.